South America's most venomous spiders

Of the 35,000 species of spiders described worldwide (out of an estimated 170,000 species), only a handful are considered to be dangerous and only 27 are known to have caused human fatalities.

Though most people have a big fear of spiders, it seems that venomous spiders are not such a big threat to humans as many people believe.

First of all, studies have shown that most serious bites attributed to spiders were, in fact, due to other causes, notably other arthropods. Secondly, antivenin against spider bite has become very effective and thus made the occurrence of death resulting from a spider's bite a very rare thing.Lastly, spider venom, in general, is usually almost harmless to humans, since it evolved for capturing or killing small invertebrates and not big mammals like ourselves.

There are, however, a few exceptions, and bites from certain species can cause severe dermatological lesions and other symptoms which require urgent medical treatment and care.

South America is home to the world's smallest spider, the world's largest spider, and to some of the world's most dangerous spiders as well.

1. Wandering Spiders, Armed Spider, Aranha Armadeira (Phoneutria)

These spiders belong to the family of Ctenidae. They live in tropical and sub-tropical America.

Phoneutria spiders can measure 30 mm and have leg span of 150 mm. Those spiders don't make a web; they hunt during the day. At night, they shelter between clothing, under furniture, in shoes or in banana bunches... A proximity to humans which is a reason for the relatively frequent occurrence of bites.

They are aggressive spiders which don't run away when disturbed and rather defend themselves by attacking: they stand on their two pairs of hind legs, lifting the fore-legs open, their red chelicerae ready to strike. They are agile and fast, capable of climb rapidly upwards the stick that is attacking them.

South American Wandering Spiders administer painful bites, though severe envenomation is very rare.

South American Wandering Spiders have a neurotoxic venom which acts on the nervous system and on the muscles. Bites cause an intense pain, which spreads through the body. Neurogenic shock can happen, especially in children and is characterized by cold sudoresis, agitation, salivation, priapism and even death. However, cases of severe envenomation are very rare.

This species occurs in the central-western, southeastern and southern parts of Brazil.

It is most often found in the rain forests, but sometimes also in cities, sheltering in rubbish around human habitation, or amongst foliage in banana plantations (hence one of its common names) where it sometimes bites workers harveting bananas.

This large spider has a body length of approximately 30 mm (1.3 inches) and it is considered extremely aggressive.

The Brazilian Wandering Spider is considered one of the most dangerous spiders in South America, and possibly the most venomous spider in the world. It has such a strong neurotoxic venom that only 0.006mg will kill a mouse. In the 1970's, this spider was responsible for more than 7,000 hospitalizations. There is currently no antivenin available. Victims must get medical attention immediately or death may soon follow.

Brazilian and American scientists have recently discovered another weird effect of Wandering Spiders bites: apparently, some South American men, bitten by the wandering spider, experienced painful , lasting erections, symptoms similar to the effects of Viagra. The scientists suspect that the toxin "Tx2-6", found in the spider's venom, is responsible.

Other species of Phoneutria include:

- Phoneutria bahiensis: found in Brazil

- Phoneutria boliviensis: found in Central and South America

- Phoneutria fera: found in the Amazon region, in Ecuador, Peru, Brazil, Surinam, and Guyana. This species is also responsible for a number of clinically important accidents.

- Phoneutria reidyi: found in the Amazon region in Venezuela, Peru, Brazil, and Guyana. It is responsible for a number of clinically important accidents.

2. Black Widows (Latrodectus)

The name black widow originates from the idea that the male is eaten after mating but this is uncommon in the field.

The genus Latrodectus contains around thirty described species and belongs to the large family Theriidiidae. Black Widows occur on all continents, except Antarctica and are mostly common in tropical and sub-tropical regions.

The female spider is 12 - 16 mm long while males are 4 - 5 times smaller.

Black Widows are rarely found indoors. They are active during the day. The female spins a messy three-dimensional web in protected corners of fields, gardens, near stones and woodpiles and in vegetation, in which she hangs upside down. The male spider does not produce a web and is not considered dangerous for humans.

Bites of the females of Latrodectus are often initially painful but are also sometimes not felt. In 50% of hospitalized cases, a severe pain lasts from one to three days. The use of antiserum may shorten the duration of the symptoms but is usually not required. Analgesics, myorelaxants and calcium gluconate are used to relief the symptoms.

The fear for this spider, often considered deadly is, however, exaggerated. Indeed, since 1954 it hasn't been responsible for any fatal bite cases in Australia, nor since 1983 in the USA, and there has never been a reported death by these spiders in the rest of the world. Besides, the Black Widow is not an aggressive spider.

Black Widow species found in Central and South America are:

- Latrodectus antheratus: found in Paraguay, Argentina

- Latrodectus apicalis: found in the Galapagos Islands- Latrodectus corallinus: found in Argentina- Latrodectus curacaviensis: found in the Lesser Antilles, South America- Latrodectus diaguita: found in Argentina- Brown Widow, Grey Widow or Brown Button Spider (Latrodectus geometricus): found virtually worldwide, including in South America- Latrodectus mirabilis: found in Argentina- Latrodectus quartus: found in Argentina- Latrodectus variegatus: found in Chile and Argentina

These spiders belong to the family Sicariidae. The genus Loxosceles comprises some 100 species found from temperate southern Africa northward through the tropics into the Mediterranean region and southern Europe, and from temperate and tropical zones of North and South America and China.

Recluse Spiders have six eyes, when most spider species have eight. They have long legs and a body that measures roughly 9 mm, are almost hairless with a violoin-like dark pattern on the dorsal side of the cephalothorax.

Recluse Spiders are nocturnal and often live near buildings, or even inside, where they shelter in clothing, bed sheets and blankets.

Bites occur mostly at night and are painless, the first symptoms being felt some 6 to 8 hours after.The injected venom can cause necrosis often accompanied by fever, haemolysis, thrombocytopenia and acute renal failure. The best therapy for victims may be the conservative use of simple first aid and local wound care.

Bites are probably less common than thought, though, since a number of bites attributed to these spiders are actually caused by other arthropods.

South American Recluse Spider species include Loxosceles intermedia, Loxosceles gaucho and Loxosceles laeta, living in Brazil, which are all very toxic, especially Loxosceles laeta.

4. Patu Digua (Patu digua)

This Colombian species is world's smallest spider, with a leg-span of 0.015 inches. It is known to be quite aggressive and is considered potentially dangerous. Yet, it is so small that experts argue about how potent its venom actually is for humans.

5. Tarantulas (family Theraphosidae)

Tarantulas are a very big group of more than 840 species. They are widely distributed worldwide, in southern and western North America, throughout South America and Africa, in large parts of Asia, all over Australia and in southern Europe.

They like warm climates, from dry hot semi-deserts to humid rain forests. Most are terrestrial and live in burrows, but some are arboreal.

Tarantulas are venomous but not dangerous to humans in general, though the genus Poecilotheria and Stromatopelma, notably can be dangerous to humans. Bites can be painful an coma has even occured after a bite from a Poecilotheria but, so far, Tarantulas have never causes a human fatality.

The South American Tarantulas can reach more than 20 cm in length and are amongst the world's largest spiders (significantly bigger than their North American counterparts). They are large enough to eat birds and are said to even attack chickens in some cases. However, In parts of South America, children sometimes keep tarantulas as pets.

5.1. Psalmopoeus

This genus occurs in Central and South America including the West Indies.

These species are believed to be relatively venomous.

- Panama Blonde (Psalmopoeus pulcher)

This spider, found in Panama, is one of South America's most dangerous spiders. This spider tends to burrow, especially when it is young. Though it might be a little less aggressive than other species, it is a very dangerous contender when challenged.

- Psalmopoeus cambridgei

This species is found in Trinidad.Research has shown that its venom is similar to capsaicin, the molecule causing irritation in chili peppers. These molecules activate sensory cells to send pain signals to the brain.

Other species of Psalmopoeus are:

- Psalmopoeus affinis: found in the West Indies- Psalmopoeus ecclesiasticus: found in Ecuador- Psalmopoeus emeraldus: found in Colombia- Psalmopoeus intermedius: found in Panama- Psalmopoeus irminia: found in Venezuela- Psalmopoeus maya: found in Belize- Psalmopoeus plantaris: found in Colombia- Psalmopoeus reduncus: found in Costa Rica- Psalmopoeus rufus: found in Panama- Psalmopoeus langenbucheri: found in Venezuela

This species can be found in French Guinea, Surinam and Brazil.It is probably the world's largest spider, its leg-span reaching up to 25 cm (11 inches) with a body length of around 9-10 cm. The males often have the largest legspans, but the females tend to be heavier (up to 150 g). The Goliath Bird-eating Spider is considered one of the most dangerous spiders of South America. It is an extremely aggressive spider known to attack humans in certain situations. Bites cause an intensive pain, miscoloration at the place of the bite. The pain usually lasts 1-2 days.

Sources:

http://www.entomon.net/venomous-most-deadly-spiders-kevlar-webs.htmVenomous and Most Deadly Spiders

http://venomous-spiders.nanders.dk/mostpoisonous.htmMost poisonous spider in the world

http://spiders.ucr.edu/dermatol.htmlBites and Stings of medically important venomous arthropodsRichard S. Vetter and P. Kirk VisscherDepartment of Entomology, University of CaliforniaPublished in the International Journal of Dermatology, volume 37, page 481-496, July 1998,